Problem: $5kl + 6km - 9k + 4 = 5l - 9$ Solve for $k$.
Solution: Combine constant terms on the right. $5kl + 6km - 9k + {4} = 5l - {9}$ $5kl + 6km - 9k = 5l - {13}$ Notice that all the terms on the left-hand side of the equation have $k$ in them. $5{k}l + 6{k}m - 9{k} = 5l - 13$ Factor out the $k$ ${k} \cdot \left( 5l + 6m - 9 \right) = 5l - 13$ Isolate the $k$ $k \cdot \left( {5l + 6m - 9} \right) = 5l - 13$ $k = \dfrac{ 5l - 13 }{ {5l + 6m - 9} }$